Upon further reflection, I was just thinking that it was a while since we got flung in the bilges - should we "start" something? I don't think I could manage any personal abuse, but I'm sure I could rise to some innuendo, it being Saturday night and all .

I missed this mate. Must have gone past it and onto the next opening. No offence but the next opening was allot tighter and helped me release my tension allot quicker.

I forgot to mention that the engine was running fine before all this. And after I'd fitted the new cables and before this problem started I launched the boat and started the engine with out problems. Then this started to happen soon after.

I'm really sh!t at electrics!
Found a wiring diagram of a Starter solenoid on line that is a bit like the one on my Yam as far as where the ignition connects to the battery lead.
How the hell does the ignition lead not burn out connected to such a high current lead???

Here's what going on inside:

The solenoid has a large switch (basically) that is either supplying power to the starter or not. In and out are on the sides in your pic. Normally, it is open (not supplying power.)

That switch is controlled by the other two wires (coming out the bottom in your pic); those wires are run through a coil that lies between the wires. Inside that coil, floating free, is a magnet. That magnet has contacts that bridge the big-ass switch that controls the power.
When the keyswitch is off, no current flows through the coil, and the contacts do not bridge the switch.

Turn the key on, and current flows through the coil, essentially making it an electrmagnet. That drives the magnet up into the switch, and the solenoid starts supplying power.

The switched line sees very little current (just enough to energize the coil). The magnet and attached contacts are the things that see high current.

That's what a solenoid does: Allows control of high current conductors with small current controls.

The solenoid has a large switch (basically) that is either supplying power to the starter or not. In and out are on the sides in your pic. Normally, it is open (not supplying power.)

That switch is controlled by the other two wires (coming out the bottom in your pic); those wires are run through a coil that lies between the wires. Inside that coil, floating free, is a magnet. That magnet has contacts that bridge the big-ass switch that controls the power.
When the keyswitch is off, no current flows through the coil, and the contacts do not bridge the switch.

Turn the key on, and current flows through the coil, essentially making it an electrmagnet. That drives the magnet up into the switch, and the solenoid starts supplying power.

The switched line sees very little current (just enough to energize the coil). The magnet and attached contacts are the things that see high current.

That's what a solenoid does: Allows control of high current conductors with small current controls.